The present invention relates to a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine.
In general, a pump unit comprises a pump body; a head assembled on the pump body; a pumping piston housed inside the head; a cylinder which houses the pumping piston; an intake valve having a valve body housed inside a seat formed in the head; and a delivery valve.
The valve body is fixed to the seat by means of threaded means which mate with the inner walls of the seat. In particular, the pump body comprises a connector which has a threaded, outer, side surface and is housed inside the seat after the valve body has been inserted. The connector keeps the valve body in contact with the head. The connector is fixed to the inner side surface of the seat by means of a threaded connection provided with a threaded surface formed on the threaded, outer, side wall of the connector and another threaded surface formed on the inner side wall of the seat.
One of the main drawbacks of the prior art consists in the fact that, in order to form the threaded surface on the inner side wall of the seat, fairly long and costly precision-machining operations are necessary. Moreover, the said threaded surfaces thus formed may give rise to wear and problems of leak-tightness during the working life of the pump because the forces which they must be withstand are high.